I know the answer to this one well! The last 2 trips, my dd got a case of the "chickens" and would want to go on every single ride until it was our turn to ride and then change her mind. Every ride has an out at the last minute without having to go back through the line. That is awful to have to walk through the crowds waiting to go in.
The only one that was problematic was Pirates (yep, refused to do Pirates but has done it hundreds of times before!!) That one we had to walk across the boat seats to the other side to exit and then they loaded others in those seats. Also, they do not let you wait right there at the exit for the rest of your party, we had to "clear the area" but every other ride I can think of, you can stand in line the whole way and then exit. She will do the Haunted Mansion so I am not sure if you can go into the stretching room and then refuse to ride but you can always go up to the door and there is an exit on the side.
Try each thing at least one time!! You might be surprised how fun something is that you are afraid of (well, except Tower of Terror-skip that if you are chicken!)